Diagnostic
Features of Phylum Echinodermata
1.
Free living exclusively marine forms.
2.
Adults are radially symmetrical while larvae are bilaterally symmetrical.
3.
Body is represented by a central disc which distinguishable into oral and
aboral surfaces
4.
Disc may bear extensions called arms.
5. Body
triploblastic, coelomate without segmentation, head and brain.
6. The surface of the body
is covered by calcareous ossicles or plates, often bearing tubercles or spines
called pedicellaria.
7.
On the
underside are five grooves called ambulacra, radiating from the mouth to the
tip of the arms,
8. They possess endoskeleton in the form
of calcareous plate called ossicles embedded in the dermis.
9. Endoskeleton
mesodermal
10.
A unique water vascular system is present. which performs many functions.
11. Digestive
system is complete. Digestive
canal is a coiled tube , anus placed on the aboral side.
12. Presence of tubular contractile tube feet or podia used as locomotory organ and/or feeding organ.
12. Presence of tubular contractile tube feet or podia used as locomotory organ and/or feeding organ.
13.Tube feet are extended and retracted by
variation in hydraulic pressure of the fluid in them and contraction of
their muscles.
14. Haemal
circulatory system poorly defined.
15. There are no
definite respiratory and excretory systems
16. Nervous
system has a central nerve ring with five radiating nerves.
17. Reproduction
is sexual. gonochoric
(Sexes are separate).
18. Gonads simple in nature.
Fertilization external. Development is indirect.
19. Development deuterostomatous,
with bilaterally symmetrical, free swimming larval forms
20. Show very high power of regeneration.
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Classes-
Asteroidea, eg. Asterias;
Ophiuroidea, eg. Ophiothrix;
Echinoidea, eg. Echinus;
Holothuroidea, eg. Sea
cucumber,
Crinoidea,
eg. Sea lily.
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